Where can I get Blender test builds?
GIT/Development builds:


The Buildbot:
There is a buildbot that builds from the git repo daily. You can get git (development) builds for all operating systems that blender supports here.
Compile from source:
Another option is compiling blender from source, see the wiki. While this may seem like a lot of effort, once its setup, it can be less trouble then having to continually download large files, and you can test new features minutes after they're committed.


Release candidates:

You can get past releases and current test-builds/release candidates here.

Linux:

There are some additional options for linux besides GraphicAll.org and the ones listed above.


Ubuntu:
You can use a PPA such as the irie PPA. (See this question on AskUbuntu for instructions)
Archlinux:
The blender-git package in the AUR